Fuel injection systems including fuel pumps with a positive displacement piston and rotary distributor valves are known in the art. One example of such a fuel injection system is shown in U.S. Pat. No. 4,621,605 to Carey, Jr. et al. and assigned to Dummins Engine Company, Inc., the assigneee of the present invention. Basically, the disclosed fuel injection system includes a fuel pump having two piston assemblies, one of which forms and delivers pre-metered slugs of fuel to unit injectors, and the other of which delivers pre-metered slugs of timing fluid to the unit injectors. Such a system is more complex than a basic single piston pump delivering only injection fuel to the unit injectors; however, the inclusion of a timing pump simply requires the use of two similar pistons and control mechanisms.
To control the piston movement in the system disclosed in the above identified Cary, Jr. et al. patent, a means is provided to stop the piston travel at one end of its stroke in an adjustable manner so that the amount of fuel metered for either injection fuel or timing fuel can be accurately and precisely controlled. Specifically, the length of the stroke of each of the pistons is set by an adjustment control means that varies the volume of fuel and timing fluid slugs on a cycle by cycle basis during operation of the internal combustion engine within which such a fuel pump is associated. Disclosed generally in the Carey, Jr. et al. patent is a movable stop arm for each piston attached to a suitable control mechanism. No specific control mechanism is disclosed; however, the patent teaches that the control mechanism associated with each adjustment control means can be mechanical, electrical, hydraulic, or the like, and can be adjusted on a cycle by cycle basis to control the pre-metered volume of the fuel and timing fluid slugs formed and delivered by the fuel system. Moreover, the injection fuel movable arm can be adjusted and controlled independently of the timing fluid stop arm.
Hydraulic control shafts and mechanisms used in conjunction with a positioning device are also known in the art. Particularly, such devices operate to control fluid flow, and have been designed with helical control surfaces provided on a control shaft which are associated with various supply and drain passages. However, prior art devices of this type utilize the helical control surfaces as a means for controlling the connection and amount of fluid flow between passages by both rotational and axial movement of the control shaft, and do not use a helical control surface to provide the axial positioning of the control shaft as determined by the rotation position of the control shaft. An example of such a control shaft with a helical control surface, wherein the shaft is both axially movable and rotationally movable, is shown in U.S. Pat. No. 4,550,702 to Djordjevic. Disclosed is an axially and rotationally movable control shaft including a helical control edge. The fluid chamber associated with the control edge permits communication between a plurality of spill passages, whereby communication between the spill passages is controlled by the axial and rotational position of the control edge. Moreover, the rotational position of the control shaft along with the axial position of the control shaft control the timing and amount of fluid communication between these spill passages. However, and as typical in the prior art, the axial movement of the control shaft is controlled by a fluid chamber having an independent fluid supply acting on a flat end of the control shaft wherein fluid pressure in the chamber urges the control shaft in one direction and in the opposite direction by a mechanically driven pin. The axial position of the control shaft does not depend on the rotational position of the helical control edge.
The basic recognition of the use of rotary positioning of a control shaft in conjunction with axial positioning of the control shaft is also disclosed in U.S. Pat. No. 4,505,244 to Smith, also assigned to Cummins Engine Company. This device includes a helical type control surface which controls fluid flow between a plurality of passages as determined by the rotary position of the control shaft. The control shaft is also a fuel plunger providing metered fuel to a fuel injector. However, as with above identified prior art, the rotary position of the control shaft does not determine the longitudinal or axial position of the control shaft. The rotary position simply determines the timing and amount of fluid flow between fuel passages due to the length of grooves formed on the control shaft body associated with the helical control surface.
In a similar manner, a fuel metering valve is disclosed in U.S. Pat. No. 4,266,571 to Bauder, wherein a helical groove is provided that connects fuel passages and the fluid flow is controlled by rotational positioning of the shaft.
Other U.S. Patents exhibiting an angled or helical control surface on a rotary and axially movable control shaft are known, such as U.S. Pat. No. 4,092,964 to Hofer et al. and U.S. Pat. Nos. 4,406,263, 4,501,246, and 4,696,271 to LeBlanc. These references basically use the rotary position of a control shaft in conjunction with the axial positioning of the control shaft that is provided with angled surfaces for controlling fluid flow between plural passages. None makes use of an angled or helical control surface to axially position such a control rod. Another, U.S. Pat. No. 4,764,092 to Thornthwaite, incorporates the use of rotary position and axial position in a control shaft without an externally provided helical or angled surface, but instead uses an internal passage with inlet and outlet ports axially displaced. Basically, such an internal passage functions similarly to the external angled surface disclosed in the above-noted prior art.
Further with respect to fuel injection systems utilizing a piston or shuttle type system including an adjustable stop, the U.S. Pat. Nos. 4,478,188 and 4,407,250, to Eheim and Eheim et al., are noted. Disclosed in these patents are combinations of hydraulic, mechanical and electrical means for positioning stop elements to control metering of fuel from a fuel supply piston. However, there is no disclosure of positioning the stop member in a hydraulic manner that specifically makes use of an angled or helical control surface.
In short, the prior art has failed to show a simple and highly accurate means to control a stop position based o the hydraulic positioning of the stop member that is suitable for use in a fuel injection system.